Heavy oil hydrocracking process



United States Patent 3,544,447 HEAVY OIL HYDROCRACKING PROCESS Roger P. Van Driesen, Hopewell, N.J., assignor to Cities Service Research and Development Company, New

York, N.Y., a corporation of Delaware Filed Dec. 19, 1967, Ser. No. 691,887 Int. Cl. C07c 3/42; C09k 3/02; C10g 9/16 US. Cl. 208-48 Claims ABSTRACT OF THE DISCLOSURE A method for preventing fouling of petroleum refinery apparatus is disclosed herein, by which polymerization of polymerizable components of high boiling hydrocarbon liquid streams from a hydrogenation treatment of heavy hydrocarbon oil is substantially eliminated. The method comprises, reducing the pressure of the high boiling hydrocarbon liquid stream, and no later than immediately after the pressure reduction, contacting the high boiling hydrocarbon liquid stream with a cool liquid hydrocarbon stream, the resulting contacted stream having a temperature up to 650 F. Preferably, two separate streams are passed out of the hydrogenation treatment zone, one being a gaseous effluent stream and the other being the high boiling hydrocarbon liquid stream. The gaseous effluent stream is cooled and partially condensed, mixed with the quenched (contacted) stream, and passed to a gas-liquid separator, after which a quantity of the separated liquid, a liquid oil stream which is the product and corresponds in characteristics to a synthetic crude oil, is recycled as the cool liquid hydrocarbon stream and mixed with the high boiling hydrocarbon liquid stream, preferably immediately after the pressure of the high boiling stream is reduced. The coincident rapid cooling of the mixed high boiling and cool liquid hydrocarbon streams immediately after pressure reduction substantially eliminates polymerization of the mixed streams and prevents rapid fouling of refinery equipment such as heat exchangers, cooling coils, and other apparatus.

CROSS-REFERENCE TO RELATED APPLICATION This application is related to application Ser. No. 693,342, field Dec. 26, 1967, by the inventor herein for -Hydrogenation of Heavy Hydrocarbon Oil, involving heat exchange between liquid streams.

This invention relates to the treatment of heavy hydrocarbon oils, particularly those subjected to a hydrogenation process. Hydrogenation processes for the conversion of heavy hydrocarbon oils to more desirable products are generally well-known in the art. Hydrogenation has been found to be particularly applicable to the treatment of heavy hydrocarbon oils wherein the treatment is carried out at a high pressure, preferably, above 1000 p.s.i.g. and at a high temperature normally above 650 R, either with or without the presence of catalysts. Such processes have resulted in improved yields of desirable products, such as naphtha and gasolines for a given amount of feedstock. An example of such a hydrogenation process is described in US. Pat. No. 3,215,617 for Hydrogenation Cracking Process in Two Stages, issued Nov. 2, 1965, to W. E.

Burch and R. P. Van Driesen, the inventor herein.

Subjecting heavy hydrocarbon oils to high temperatures without the accompanying high hydrogen pressures would result in thermal degradation, undesirable cracking, polymerization, and added coke. While hydrogenation processes, such as that described above in US. Pat. No. 3,215,617, generally call for maintaining high hydrogen pressures along with the high temperatures within the reaction zone, the liquid reaction products contain polymerizable constituents which will, when passed out of the "ice reaction zone, tend to polymerize. It has been generally thought that the conditions present in such hydrogenation streams will minimize polymerization and coking as the stream conditions are similar to hydrogenation zone conditions, there being hydrogen available to saturate any thermally cracked molecules. However, any polymerization poses a severe problem for refinery equipment, and obviously results in reduction in yield. The polymerized material rapidly builds up, based upon high quantitative flow rates, and severely clogs, renders inefiicient and sometimes inoperative, various refinery equipment. Accordingly, it is, therefore, advantageous to overcome these problems in the prior art.

I have discovered a method for reducing fouling of refinery equipment in a hydrogenation process wherein heavy hydrocarbon oil is treated with hydrogen at a high pressure and a high temperature and results in a gaseous efiiuent stream and a high boiling hydrocarbon liquid stream having polymerizable constituents. The method substantially eliminates polymerization of the polymerizable constituents by reducing the pressure of the high boiling hydrocarbon liquid stream and no later than immediately after the pressure reduction, contacting the high boiling hydrocarbon stream with a cool liquid hydrocarbon stream to result in a temperature of up to 650 F. for the contacted streams.

Accordingly, it is an object of this invention to provide a method for retarding the polymerization of high boiling hydrocarbon polymerizable constituents during the processing thereof.

Another object of this invention is to provide a refinery process for substantially eliminating the formation of polymerization materials in hydrocarbon oil product streams in order to reduce fouling of refinery equipment.

Another object of this invention is to provide an improved method for the catalytic hydrogenation of hydrocarbon oils at high pressure and high temperatures.

Other objects and advantages of the method of this invention will become apparent from the description of the drawings and preferred embodiments which follow.

Heavy hydrocarbon feeds such as residual fractions are generally subjected to hydrogenation treatment under severe conditions of temperature and pressure. Such feeds are reacted with hydrogen in the presence of catalysts at temperatures above 650 F. and pressures preferably between 1000 and 3000 p.s.i.g. in order to convert heavyhydrocarbon oil having high molecular weight, mostly unsaturated hydrocarbon molecules to lower molecular weight, lower boiling more saturated hydrocarbon oils. The cracking that takes place during hydrogenation is primarily due to thermal effects, but because of the presence of a high hydrogen partial pressure and the hydrogenation catalyst, there is also, a suppression of polymerization which would normally occur and result in considerable coking as in the usual thermal-cracking processes.

The products of the hydrogenation reaction are usually removed as two streams, one being a low boiling mostly saturated gaseous efiiuent stream, and the other being a higher boiling liquid hydrocarbon stream containing unsaturated molecules. The lower boiling effiuent stream is cooled and reduced in pressure and separated into light oil liquid fractions and gaseous fractions. In the process according to this invention the higher boiling hydrocarbon liquid stream is passed at the reaction pressure and temperature to a pressure reducer where the liquid stream is contacted either before, during or immediately after the pressure reduction, with the aforementioned cool light oil liquid fraction so as to rapidly reduce the temperature of the high boiling liquid hydrocarbon stream toa temperature, e.g. 650 F., below which thermal cracking and polymerization will occur to a significant extent. While reducing the temperature of the high boiling hydrocarbon stream to a temperature below about 650 F. is satisfactory, a reduced temperature of about 550 F. is preferred. The cool oil liquid fraction, hereinafter referred to as the cool hydrocarbon liquid product stream, is an oil stream boiling above 550 F. which is obtained as product from the hydrogenation process described herein by mixing the cooled gaseous effluent stream with the stream resulting from the mixture of the cooled hydrocarbon liquid stream with the high boiling hydrocarbon liquid stream from the hydrogenation reaction, cooling the mixed stream and subjecting it to gas-liquid separation, the separated liquid stream being the cool hydrocarbon liquid product stream, preferably below temperature of about 550 F. Thus, also contemplated and described as an embodiment of the process of this invention, is the use as the contacting stream of the cool hydrocarbon liquid stream which results from the mixing of two streams of the hydrocarbon liquid product stream from a point immediately after gas-liquid separation and another point after cooling by the feed and therefore at different low temperatures. As such, the temperature of the cool hydrocarbon liquid product stream is not dependent upon that present'at a single stage of the process, and therefore is controllable within the limits imposed by both stages. It is preferred that the high boiling hydrocarbon liquid stream be contacted with the cool liquid hydrocarbon product stream immediately after the pressure of the high boiling stream is reduced. Mixing the high boiling hydrocarbon and cool hydrocarbon liquid product streams immediately after the pressure of the former stream is reduced is preferred for several reasons. The pumps and piping required to raise the pressure of the cool stream to that of the high boiling hydrocarbon stream need not be high pressure equipment. Additionally, mass flow across the pressure reducing means is lower. Thus, simpler, cheaper, more easily maintained equipment is required and desired temperature is obtained by varying the quantitative rate of flow of each of the separate liquid product streams.

To facilitate understanding of the present invention, reference is made to the accompanying drawings which diagrammatically represent the process. Heavy hydrocarbon feed enters the process through conduit 12. The feed may be any suitable hydrocarbon oil, preferably one boiling in the range between 350 F. and 1100" F., and may include e.g., virgin or thermal naphtha, catalytic cracking naphthas, cycle oils, virgin or thermal gas oils, coker distillate, vacuum gas oils, deasphalted gas oils, and any other fractions derived from crude oil or from naturally occurring tars, shale oils or from synthetic crude produced from petroleum residuum, natural tar, shale oil, tar sand or coal. Relatively heavy, hydrocarbon oils boiling above 650 F. are especially suitable for treating according to this process. The feed normally at about 200 F., is passed through a preheater 14 which serves the dual purpose of heating the feed to a temperature of about 430 F. and of concurrently cooling the process hydrocarbon liquid product stream described hereinafter from about 550 F. to 350 F. The preheated feed is 1 passed through conduit 16 to an efiluent condenser-exchanger18 where the feed is further heated to about 780 feed pipe 20 where it is mixed with the heated feed in ,the amount between about 1000 and about 50,000 stand- .ard cubic feet (s.c.f.) of hydrogen per barrel of feed, a preferred rate being above 6000 s.c.f. of hydrogen per :barrel of feed.

' The mixed feed and hydrogen gas are subjected to a temperature of between 650 F. and 900 F. and pressures between 750 p.s.i.g. and 4,000 psi-g. in a hydrogenation zone'26. A suitable hydrogenation catalyst is employed within the hydrogenation zone 26. Such hydrogenation catalysts are well-known, examples being cobalt, iron, molybdenum, nickel, tungsten and cobalt molybdate. These catalysts, including their oxides and sulfides, may be used alone or in combination with each other, and, of course, may be supported on various bases, such as alumina, silica, or alumina-silica. The hydrogenation zone 26 may comprise either fixed bed, fluid bed, or ebullient bed type catalytic reactors. An example of a suitable hydrogenation reactor for use as the hydrogenation zone 26 is shown in US. Pat. No. 3,278,420, issued Oct. 11, 1966, to J. M. Jaeger. While one hydrogenation zone 26 is shown in the drawings it is contemplated, as within the scope of this invention, that such hydrogenation zone may encompass more than one hydrogenation reactor or stage, and in such event, those processes having more than one hydrogenation reactor are operated in series, utilizing the output of one reactor as the feed for a second hydrogenation reactor.

Hydrogenation reaction products are removed from the hydrogenation zone 26 in two separate streams. One stream comprising gaseous low boiling hydrocarbons, passes out of the hydrogenation zone by gaseous eflluent conduit 28, to the condenser-exchanger 18 where the gaseous efiluent is first condensed and cooled at high pressure by heat transfer to the feed oil stream. The condensed effluent stream is passed through piping 30 to a gas-liquid separator 32 where pressure is reduced and the gas and liquid are separated as gaseous hydrocarbon and light liquid cycle oil at a temperature of about 550 F.

The second stream from the hydrogenation reactor, comprising high boiling liquid hydrocarbons at high temperature (above 650 F.) and high pressure (e.g., above 1000 p.s.i.g.) passes out of the hydrogenation zone 26 by conduit 34 to a pressure and temperature reducing zone 36 where the high pressure is substantially reduced by conventional means, such as a throttling valve 38 while immediately thereafter the temperature is rapidly reduced (quenched) in mixing zone 40 by mixing the high temperature liquid stream with a cooler stream of cool liquid hydrocarbon product obtained as hereinafter described from the hydrogenation process. A sufficient quantity of the cool liquid hydrocarbon product oil is passed to the mixing zone 40 for the purpose of acting at the quenching liquid and mixed with the high temperature heavy hydrocarbon liquid thereby. obtaining a mixed liquid hydrocarbon stream at sufiiciently low temperature to substantially eliminate thermal cracking and polymerization of the heavy hydrocarbon molecules in the mixed stream. While it is particularly preferred to mix the cool liquid hydrocarbon product stream with the high temperature stream immediately after the pressure of the high temperature stream is reduced, the streams may be mixed prior to, or simultaneously with the reduction of pressure. In both the latter instances, the cool liquid hydrocarbon product stream would have to be pumped utilizing a high pressure pump to the high pressure side of the pressure and temperature reducing zone 36. In addition to requiring a high pressure pump and piping, the pressure and temperature reducing zone 36, will have to accommodate the larger fluid mass flow of the mixed hydrocarbon streams.

If the temperature is not rapidly reduced immediately after the point at which pressure is reduced then thermal cracking and coincident polymerization in the hydrocarbon liquid stream would occur. This cracking and polymerization is in suflicient quantity to severely affect the operating effectiveness of process units, such as piping, valves and particularly heat exchangers, by depositing the polymerized material on the walls thereof. Verysinall amounts of such polymerization material in the relatively large amounts of hydrocarbon liquid passing through such process units are suflicient to rapidly foul and render them inoperative or inefliective. This is particularly true of heat exchanger units wherein the stream of hydrocarbon liquid passes through bundles of tubes and any polymerization materials will deposit on the walls of the tubes and result in inadequate heat transfer, additional polymerization and rapid fouling of the exchanger.

As shown in the drawings, a portion of the stream of liquid product oil is recycled from the separator 32 as the cool liquid hydrocarbon stream through conduits 41, 42, 43 and 44 and pump 46 to the mixing zone 40 where the recycled cool stream is mixed with the high boiling hydrocarbon liquid stream to rapidly reduce the temperature of the resultant mixed hydrocarbon stream. Conduit 41 is connected at its upstream end to the separator 32 and at its downstream side to the preheater 14. Conduit 42 connects conduit 41 to the inlet of pump 46 and conduit 43 connects the pump outlet to conduit 44 which is connected to its downstream end to the mixing zone 40. A conduit 47, through which the product, a hydrocarbon oil having the characteristics of a synthetic crude oil is withdrawn, is connected to the heating fluid outlet of the preheater 14. A conduit 48 connects the product withdrawal conduit 47 to the conduit 44 which in turn connects to the mixing zone 40. A pump 50 is mounted in conduit 48. Alternatively a portion of a second lower temperature (i.e., 350 F.) liquid product oil stream in suflicient quantity to obtain a mixed hydrocarbon oil stream having a temperature of up to about 650 F. can be recycled as the cool liquid hydrocarbon stream from the preheater 14 through conduit 48 and pump 50 to the mixing zone 40 and mixed with the high boiling liquid hydrocarbon stream. Depending on the process operating conditions, the operator may select a portion of either low temperature liquid product oil streams as a source of the cool liquid hydrocarbon stream, and mix them to obtain the desired low temperature. Valves 52 and 54, respectively, provide means for controlling the source, quantity and coincidentally the temperature of the recycled cool liquid hydrocarbon streams. Thus, equal quantities of the first and second low temperature liquid prod uct oil stream can be metered through valves 52 and 54 in order to obtain a cool liquid hydrocarbon stream having an intermediate temperature. If the temperature of the first recycle liquid oil stream is about 550 F. and that of the second about 350 F., a cool liquid hydrocarbon stream having a temperature of about 450 F. would result. The process, therefore, provides a means of varying the temperature of the cool liquid hydrocarbon stream and of the resultant mixed liquid hydrocarbon stream.

The mixed liquid hydrocarbon stream is passed out of the pressure and temperature reducing zone 36 by conduit 56 and through aftercooler 58 where the temperature of the mixed liquid stream is reduced by heat transfer with a coolant from a source, not shown, to the temperature of the cooled eilluent stream and passed by way of conduit 60 to piping 30 where it is mixed with the cooled efiluent stream.

The portion of the low temperature liquid product stream from the separator 32, not recycled to the pressure and temperature reducing zone 34, is passed to the preheater 14. At the preheater 14, the heat is first transferred to the feed and the cooled stream passed out as the product or the second cool liquid product oil stream, a portion of which may be recycled as described above to the mixing zone 40, according to the method of this invention. The portion of the second liquid product oil stream not recycled is passed out of the process as product and constitutes a lower boiling improved hydrocarbon oil suitable for further processing as a synthetic crude oil. The following examples are given to illustrate the process of the present invention.

EXAMPLE I About 2500 barrels per day (b.p.d.) of API feedstock at a temperature of 200 F. are fed to conduit 12 and heated to 430 F. in the preheater 14 and subsequently heated to 778 F. in the condenser-exchanger 18. Twenty million s.c.f. of hydrogen containing gas per day are heated in the heater 22 to about 812 F., mixed with the heated feed and the resultant mixture having a temperature of about 790 F. is passed to the hydrogenation zone 26. The hydrogenation zone 26 comprises two reactors containing hydrogenation catalyst and operating in series with the efiluent from the first reactor being used as feed to the second reactor. The temperature of reaction in both reactors is about 825 F. and pressure about 3650 p.s.i.g. The hydrogenation treatment results in about 26,000 lbs./hr. of gaseous eifiuent passing out through efiluent conduit 28 at 825 F. to the condenserexchanger 18 and about 25,000 lbs./hr. of high boiling hydrocarbon liquid at a pressure of about 3640 p.s.i.g. and a temperature of about 825" F. passing out through conduit 34 to the pressure and temperature reducing zone 36. Approximately 55,000 lbs. per hour of the low temperature first liquid product oil stream at a temperature of about 550 F. from the gas liquid separator 32 is pumped as the cool liquid hydrocarbon stream to the mixing zone 40. The high boiling hydrocarbon liquid is reduced in pressure from 3640 p.s.i.g. to about 200 p.s.i.g. and immediately afterwards mixed with the cool liquid hydrocarbon stream oil resulting in mixed liquid stream having a temperature of about 634 F. The mixed liquid stream is then passed through the aftercooler 50 where the temperature is reduced to about 555 F., and the low temperature mixed liquid stream is introduced into the cooled efiluent stream prior to entering the separator. By reducing the temperature of the high temperature stream from 825 F. to about 634 F., the thermal cracking and coincident polymerization and coking is substantially eliminated and rapid fouling of the aftercooler is avoided.

EXAMPLE II In this example the process followed is essentially the same as in Example I, except that no portion of the liquid product oil from the separator 32 is bled off as the cool liquid hydrocarbon stream to the pressure and temperature reducing zone 36. Rather, about 40,000 lbs. per hour of the second cool liquid hydrocarbon product stream from the preheater 14 is recycled as the cool liquid hydrocarbon stream and pumped to the mixing zone 40. The temperature of the cool liquid hydrocarbon stream is about 350 F. and upon mixing with the heavy hydrocarbon oil stream at the pressure and temperature reducing zone 36, results in about 65,000 lbs. per hour of the mixed liquid hydrocarbon having a temperature of about 533 F.

EXAMPLE III Essentially the same process is followed as in the above examples, except that 15,000 lbs. per hour each of the first and second liquid product oil stream, having temperatures of about 550 F. and 350 F., respectively, is bled otf as the cool liquid hydrocarbon stream to the mixing zone 40. The resultant mixed stream has a temperature of about 620 F.

Besides substantially eliminating polymerization of the polymerizable constituents of the high boiling hydrocarbon liquid stream, several other advantages are obtained by employing the method according to this invention. By employing suitable quantities of the second cool liquid hydrocarbon stream, as described in Example II, the need for aftercooling may be avoided and aftercooler 58 not required. Additionally by mixing the cool liquid hydrocarbon stream with the high boiling hydrocarbon stream no later than immediately after reducing the pressure thereof, constituents of the high boiling hydrocarbon stream that would have vaporized at the lower pressure are retained in the liquid phase and provide far more efiicient heat transfer.

While the invention has been described above in connectionwith specific embodiments, it will be understood by those skilled in the art to cover those changes and modifications which may be made without departing from the spirit and scope of the invention.

What is claimed is: 1. In a hydrogenation process wherein heavy hydrocarbon oil feed is treated with hydrogen under conditions of high pressure of from 1000 p.s.i. to 4000 p.s.i.g. and high temperature of from 650 to 900 F. in a hydrogenation zone, resulting in a high boiling hydrocarbon liquid stream at said high pressure and temperature and a gaseous efiluent stream, said high boiling liquid stream having polymerizable constituents, the method for substantially reducing polymerization of said constituents which comprises: reducing the high pressure of said high boiling liquid stream to a pressure of up to about 200 p.s.i.g.

quenching said high boiling liquid stream to a temperature of up to about 650 F. no later than immediately after said reduction of the high pressure of said high boiling liquid stream by mixing said high boiling liquid stream with a sufficient quantity of aliquot portions of mixed first and second cool liquid hydrocarbon product streams, the resultant stream being a quenched stream at a temperature of up to 650 F.,

cooling said gaseous efliuent stream,

mixing said cooled gaseous efiiuent stream and said quenched stream, separating liquid phase components of said mixed efliuent and quenched stream as said first cool liquid hydrocarbon product stream,

bleeding oif a predetermined aliquot portion of said first cool liquid hydrocarbon product stream for quenching of said high boiling hydrocarbon liquid stream,

further cooling the remaining portion of said first cool liquid hydrocarbon product stream, bleeding ofi a predetermined aliquot portion of said further-cooled first cool liquid hydrocarbon product stream as a source of said second cool liquid hydrocarbon product stream for quenching said high boiling hydrocarbon liquid product stream, the remaining portion of said second cool liquid hydrocarbon product stream constituting the product of said proc: ess, and

mixing said aliquot portions of said first and second cool liquid hydrocarbon product streams prior to mixing said mixed first and second cool liquid hydrocarbon product streams with said high boiling liquid stream.

2. The method of claim 1 wherein said quenched stream is cooled prior to mixing of said mixed efiluent and quenched stream with said cooled gaseous efliuent stream.

3. The method of claim 2 wherein said step of further cooling the remaining portion of said first cool liquid hydrocarbon product stream comprises transferring heat from said remaining portion of said first cool product stream to said heavy hydrocarbon feed oil.

4. The method of claim 3 wherein said step of cooling said. gaseous efiiuent comprises transferring heat to said heavy hydrocarbon feed oil.

5. In a hydrogenation process wherein heavy hydrocarbon oilfeed is treated with hydrogen under conditions high temperature of from 650 to 900 F. in a hydrogenation zone,.resulting in a high boiling hydrocarbon liquid stream at said high pressure. and temperature and a gaseous efliuent stream, said high boiling liquid stream having polymerizable constituents, the method for substantially reducing polymerization of said constituents which comprises:

reducing the high pressure of said high boiling liquid stream to a pressure of up to about 200 p.s.i.g., quenching said high boiling liquid stream to a temperature of up to about 650 F. no later than immediately after said reduction of thehigh pressure of said high boiling liquid stream by mixing said high boiling liquid stream with a suflicient quantity of an aliquot portion of a cool liquid hydrocarbon product stream, the resultant stream being a quenched stream at a temperature of up to 650 F., cooling said gaseous efiiuent stream, mixing said cooled gaseous eflluent stream and said quenched stream,

. separating liquid phase components of said mixed effluent and quenched stream as said cool liquid hydrocarbon product stream, and

bleeding ofl? a predetermined aliquot portion of said cool liquid hydrocarbon product stream for quenching of said high boiling hydrocarbon liquid stream, the remaining portion of said cool liquid hydrocarbon product stream constituting the product of said process.

References Cited UNITED STATES: PATENTS PAUL M. COUGHLAN, JR., Primary Examiner G. E. SCHMITKONS, Assistant Examiner US. Cl. X.R. 

